The Milky Way is a barred spiral galaxy. The extension of the barred disk is
2.5-3 kpc [1]}, and the extension of the halos is \(\approx \)  100 000 pc, but some recent investigations
indicate that this might be substantial larger, \(\approx \)  300 kps or even more [2]}, [3]}.
The Milky Way rotates with a rotational
velocity \( 220 \pm 10\)  \( \textrm {km s}^{-1}\)  for stars at a distance of \( 8.0 \pm 0.3 10\)  kpc from its center [4]},
but the rotations at different distances from the
center of the galaxy deviate from calculations of
the rotation caused by the gravitational forces between its constituents, and this deviation is explained by the existence of
unknown dark matter [5]}, [6]}, [7]}.
The Milky Way contains very old stars from the period just after the ”Big Bang" [8]}, so the galaxy has presumably exist
for more than thirteen billion years. The rotational time (galactic year) of the Milky Way is
estimated to be \(\approx \)  220-240 million years, and this implies
that an old star in the Milky Way with this rotational velocity must have performed of the order \(\approx \)  60 cycles.
